Devices such as automobile radios or personal computers contain subassemblies such as cassette playing mechanisms or disk drives that are attached to the chassis using threaded fasteners. The chassis provides structural support for the subassemblies and also provides electromagnetic shielding to limit electromagnetic interference (EMI) experienced by, and/or created by the device. The fasteners ensure that each subassembly within the chassis is properly located and securely retained within the chassis.
The use of such fasteners can have numerous drawbacks, particularly in a high volume production setting. The process for applying or installing fasteners can vary, but there is usually some degree of automation required, ranging from manually loading a screw into a bit on a pneumatic driver to using self-feeding automated machines. Typically, the torque applied by the device used to drive the fasteners must be monitored regularly and adjusted in order to assure proper seating of the fasteners. When fasteners are used, sheet metal tolerances, as well as tolerances of the fasteners themselves, have to be maintained at tight levels to allow for the minimization of stress in the assembly when aligning multiple fasteners with corresponding holes in the chassis and in the subassembly.
When threaded fasteners are used to assemble an electrical device, the assembly cycle time can be very long especially in high volume production. An operator assembling the device must typically first obtain the threaded fastener, orient and position it in alignment with the driver bit, then manipulate or actuate the machine to drive the threaded fastener. Furthermore, using threaded fasteners presents a risk of any one of the following upstream failures occurring: stripping of fastener threads; insufficient torque resulting in an unseated fastener; excessive torque resulting in distension/deformation of the fastener or adjacent electrical components; installation of the wrong fastener type or size; foreign object damage due to fasteners and/or metal shavings dropping onto the assembly and/or subassembly; and stripping of the head of the threaded fastener. Also, a fastener installation tool such as a driver and bit can slip off the fastener and impact an electrical component resulting in a damaged assembly.
If self-tapping fasteners are used, the process of driving the self-tapping fasteners into sheet metal often causes shavings of sheet metal to disperse into the assembly. Such shavings have been known to cause electrical failures, such as shorts or corruption of magnetic components that can permanently damage the product. If self-tapping fasteners are not used, an extra production step is required to pre-form threads in the sheet metal of the chassis and/or the subassembly to be installed within the chassis.
Fasteners further require an additional inventory burden on the production line in that the production line must be continuously stocked with part numbers (fasteners) other than the integral components that add value to the assembly. Also special tools specifically required for assembly, using fasteners, such as drivers and bits, must be continuously monitored and maintained for proper performance, wear and torque specifications. Typically, the top and/or bottom surface of the chassis must be secured in place after the subassembly is attached to the chassis.
Special fixtures are often required on the production line to secure a subassembly in a proper location and orientation while it is mounted within the chassis with fasteners. Such fixtures can be very complex, and the use of such fixtures usually requires extra handling of both the subassembly and of the resulting assembly thereby adding to the production cycle time and potentially compromising quality of the final product.
FIG. 1 illustrates the construction of a typical prior art automotive radio/compact disc (CD) player 10. Radio/CD player 10 comprises a radio subassembly whose principle circuit components are carried on a circuit board 12 and a CD player subassembly 14. The circuit board 12 and the CD player 14 are encased within a common chassis 16 made up of sheet metal components. Chassis 16 includes a wraparound housing 18 defining a back and sidewalls, a top cover 20, a bottom cover 22 and a front plate 24 which are interconnected by numerous threaded fasteners to collectively enclose the subassemblies. The top and bottom covers 20 and 22, respectively, are provided with large arrays holes or openings for airflow and ventilation of heat generated within the radio/CD player 10. A convector or heat sink 26 is carried on an outer surface of one of the chassis sidewalls and is interconnected through a port/window 28 to a power device assembly 30. A trim plate assembly 32, along with a support pad 34 and CD dust cover 36 are affixed to the front plate 24, providing an operator control interface with the radio/CD player 10. Circuit board 12 is electrically in-circuit with the CD player subassembly 14 through an intermediate flex wire cable 38 and with the power device assembly 30 through a jumper cable 40. Information bearing labels 42 and 44 are provided for future reference by the operator and service technicians. The radio/CD player 10 is electrically interconnected with an antenna, power supply, speakers and other related systems of a host vehicle by rear-facing connectors 46 carried on the circuit board 12 which are registered with openings 48 in the rear wall of wraparound housing 18. The radio/CD player 10 is mounted within a host vehicle by threaded fasteners passing through openings in mounting features 50 extending from front plate 24 and a rearwardly directed mounting bushing 52 which is threadably affixed to a stud 54 carried on the outer surface of the rear wall 56 of wraparound housing 18. As best seen in FIGS. 11 and 12, the shank of the stud 54 extends outwardly through a hole 58 disposed concentrically with a localized recess 60 and the stud 54 is seated within the recess 60. FIG. 90 illustrates another known stud design including a threaded shank secured to the rear wall 53 of a radio set 51 by a set nut 55 and receiving a molded rubber, plastic or vinyl stud 57 thereover. Note the large number of threaded fasteners 59.
The radio/CD player 10 of FIG. 1 is of ordinary complexity and may require fifty or more threaded fasteners to complete the manufacturing process. Installation of that many fasteners may require that the in-process chassis be re-positioned/re-fixtured ten to fifteen times as it passes along an assembly line of eight to ten skilled workers/work stations.
Vehicle entertainment systems usually include an audio component such as a radio to enable receiving signals from antennas, contain various forms of playback mechanisms, and have the capacity to accept data from user devices like MP3 players. Typically, the radio has a decorative assembly that provides man-machine interface as well as displaying pertinent data relative to the selected media and audio settings. Also, the back-end or chassis is constructed of metal to provide various functions to ensure the performance of the radio in the vehicular environment. The structure to contain the mass from playbacks, the heat conductive properties, and the electrical shielding and grounding are just a few of the advantages to using the metal construction. Unfortunately, with the density of the metal, the disadvantage of added weight is a side effect of the typical construction. In a vehicle, added weight impacts fuel economy, as well as other hidden costs during assembly that can effect the cost of the product, like sharp edges of metal can be a potential hazard for assemblers in the manufacturing plant as well as added weight can limit the packaging of multiple parts in containers for inter and outer plant distribution.
Static electricity (electrostatics) is created when two objects having unbalanced charges touch one another, causing the unbalanced charge to transfer between the two objects. This phenomenon commonly occurs in homes, vehicles and other environments when the air is dry (i.e. has a characteristic relatively low level of humidity). For instance, when a person slides onto a car seat, electrons may transfer between the two, causing the surface of the person's body to store a charge. When the person, then, touches a vehicle component, the charge may travel (discharge) from the body to the component, thus creating static electricity. If the object touched is an electronic device, such as a home stereo, home theatre system, computer, vehicle entertainment system or other electronic media system, this electrostatic discharge can be harmful to the sensitive electronic components of the device. For instance, when a person slides onto a vehicle seat and inserts a disc into the car stereo, a charge may travel from the body through the disc to the sensitive electronic components in the vehicle stereo. Similar problems may occur when using DVD and other magnetic media and disc players.
Accordingly, problems with the drainage of a static electric charge impacting sensitive electronic components continue to persist.